The subject matter disclosed herein generally relates to heat exchangers, and more specifically, to wave fin structure for heat exchangers.
A typical air-to-air plate fin heat exchanger consists of a stack of inter-conductive air flow sections or layers. Hot air and cold air are forced through alternate layers (referred to as “hot” and “cold” layers, respectively, from time to time herein) in order to exchange heat. In a gas turbine blade disk cooling system, the hot air comes from the engine compressor before entering the turbine blade disks and then flows through bleed layers. The cold air is outside air and flows through ram layers in the engine fan ducts. These alternately stacked ram and bleed layers are joined together along a thermally conductive medium called the parting sheet, and heat from the bleed layers is transmitted through the parting sheets to the ram air flow. Of course, heat exchangers could receive air from other sources as well and the teachings herein are not limited to gas turbine management.
The hot and cold layers are similar and each includes an array of cooling fins and frames or closure bars which are positioned on the parting sheets to define each layer. Frames or closure bars are placed along the edges of the layers to support the ends of the parting sheets. In addition to supporting the ends of the parting sheets, theses bars close off each layer, except where there is an air inlet or an air outlet. At the air inlets and outlets the fins provide support for the parting sheets.
To fabricate the heat exchanger, the hot and cold layers are stacked alternately one on top of another. The assembly may then be places in a vacuum furnace for brazing. During the brazing process the stack is squeezed so as to force the layers together.
The above description relates to heat exchangers that may be made with what are called “low temperature” materials. High temperature heat exchanger may be required where bleed air operating temperatures that exceed the capability of conventional metals (e.g., low temperature). However, some aircraft or other situations may require compact heat exchangers include aircraft engine pre-coolers, gas power plant recuperators, and solid oxide fuel cell waste heat recovery, etc. that are in the high temperature range (T>800° C.). Widely used materials which can withstand temperature up to 700° C. are metal superalloys, such as stainless steel, inconel, and Haynes. Ceramic heat exchanger technology provides a solution to the high temperature requirements and may allow for inlet temperatures up to 900° C. However, ceramic heat exchanger development has been limited in past years due to poor thermal conductivity and high machining/manufacturing costs.